Method and apparatus for heating and drawing threads



1963 E. SIGGEL ETAL 3,099,872

METHOD AND APPARATUS FOR HEATING AND DRAWING THREADS Filed Jan. 10, 1961 FIG. 2

FIG. I

INVENTORSZ ERHARD SIGGEL FRITZ KLEEKAMM BY m aw zm M 055T ATT'YS 3,699,872 METHQD AND APPARATU FUR HEATENG AND DRAWTNG THREADS Erhard fiiggel, Laudenburg am Main, and Fritz Kleelramm, Obernbnrg am Main, Germany, assignors to Vereinigte Glanzstolf-Fabrihen AG Wuppertal-Elberfeld, Germany Filed Jan. 10, 196i, Ser. No. 87,480 Claims priority, application Germany .l'uly 4, 1959 Claims. (Cl. 28- 7133) This invention relates to a method and apparatus for heating and drawing, i.e. stretching, threads so as to impart the necessary orientation and physical properties to the fibrous structure. In particular, the invention is concerned with the improvement of the process in which a synthetic filamentary material having heat-stretchable properties is first heated at a lower drawing temperature under stretching tension and is subsequently heated at a higher fixing temperatur also under stretching tension. The improvement of the present invention is embodied in special apparatus as well as in the process itself.

It is a common practice in the manufacture of synthetic threads to subject them to drawing or stretching under tension in order to obtain certain requisite properties of tensile strength and elongation. This procedure is also referred to as filament or fiber orientation and is adequately illustrated by all of the basic references in this art. In working With polyamide filamentary materials, such as polyhexatmethylene adipamide or polycaprolactam, drawing of the polyamide thread was first carried out by the so-called cold-stretching method whereby the thread is stretched on a fixed agate rod or similar device at room temperature. More recently, it has been found advantageous to stretch polyamide threads in two stages at elevated temperatures in order to obtain better or different properties, especially a fixing or stabilization of the thermo-extensibility of the thread. For example, one practice has been to pass the polyamide thread over a first rod, heated to about 70 C., while stretching to about three times the original length of the thread and then over a second rod, heated to about 190 C., with an additional twofold stretching of the thread. The thread is thus drawn or stretched to about 500% of its original length. The two stages are carried out at different temperatures, the first stage being carried out at a temperature referred to as the drawing temperature and the second stage being carried out at a temperature referred to as the fixing or stabilizing temperature.

Because of the special physical properties of linear polyesters, e.g. polyethylene terephthalate, a cold-stretching of the threads or filaments is not possible. In this case, it is necessary to stretch the thread at a temperature in the range of the critical point of second order. Again, two-stage heating and drawing processes have been developed wherein two different temepratures are employed. For example, the threads are conducted over two separately heated rods or over a rod and a flat or curved plate as stretching elements maintained at different temperatures. With polyesters, the higher temperature is required in the second stage to fix or stabilize the thread against shrinkage.

In all of the known processes, stretching and thermal stabilization of the thread is accomplished with at least two devices, such as rods, rollers, plates or the like, each being maintained at a constant but different temperature. However, even if these two devices are positioned quite close to each other, it is impossible to avoid a cooling of the thread during its travel between stages. Also, while the thread contact surface in the first stage can be relatively small, the second or fixing stage is effective only if the ties at thread remains in contact with a heated surface which is sufiiciently large to provide an extended time for heating. The heating time in the second stage is dependent in each case upon the particular synthetic material being treated as well as the drawing speed. In general, the thread must maintain contact with the heated surface in the second stage at least long enough for the thread to reach the particular stabilization or fixing temperature at which the surface is maintained. As a result, previous apparatus for two-stage heating and drawing are relatively complicated and space consuming.

A principal object of the present invention is to provide a method and apparatus for simultaneous heating and drawing of synthetic threads in a single stage wherein it is also possible to obtain a thermal stabilization of the threads.

Another object of the invention is to heat, stretch and stabilize synthetic threads in one continuous operation in which the thread being treated is maintained in constant contact with a heated surface.

Still another object of the invention is to provide a relatively simple heating device for stretching and stabilizing threads, said device being readily adapted for combination with the usual feed and draw rolls employed to impart a stretching tension to the threads.

Yet another object is to provide a method and apparatus whereby synthetic threads can be heated and drawn to give valuable filamentary products, especially as regards their thermal stability.

These and other objects and advantages of the invention will be more readily understood upon consideration of the following detailed description together with the accompanying drawing wherein:

FIG. 1 is a top plan view and side elevational view, the latter in cross-section, of one heating device which can be employed in conjunction with the invention;

FIG. 2 is a top plan view and side elevational view, the latter in cross-section, of a second embodiment of a heating device;

FIG. 3 is a top plan view and side elevational view, the latter in cross-section, of still another and preferred embodiment of the heating device; and

FIG. 4 is a side elevational view in partly schematic form which illustrates the embodiment of FIG. 3 in combination with the remaining essential elements of heating and drawing apparatus.

In all the figures, a resistance heating element is illustrated in schematic form.

It has now been found, in accordance with the present invention, that the heating and drawing of synthetic threads together with their thermal stabilization can be accomplished in a more favorable and improved manner if the thread is simultaneously heated and drawn in spiral winding contact over the surface of an elongated body made up of substantially cylindrical crosssections, the surface being heated at progressively increasing temperatures in the direction of thread travel over the surface. The temperatures of the surface are regulated such that the usual dnawing or stretching temperature is maintained at the run-on or thread receiving end of the heated elongated body and the maximum fixing or stabilizing. temperature is preferably maintained at the run-off or thread discharge end of the elongated body. The thread is thus continuously heated in one stage while being stretched with uninterrupted contact with a single heated surface. Although the thread run-off end of the elongated body and its corresponding surface can be heated by direct heat exchange to a temperature somewhat below the maximum fixing temperature, it is preferable to employ the highest temperature possible in order to obtain optimum results.

The continuous one-stage heating and drawing of the invention can be accomplished by employing a novel combination of apparatus which includes the conventional feed and draw rolls as means to supply the thread and means to draw off the thread at a more rapid rate than it is supplied, thereby imparting a stretching tension to the thread. Between the feed and draw rolls, a special heating device is positioned or mounted, preferably on a frame common to one of said rolls, in the path of the thread as it is being drawn. The heating device is essentially an elongated, heat-conducting tube which is hollow in at least a portion of its length. In other words, the tube has a continuous outer sunface in the form of a cylinder, frustum or the like, and an inner axial bore or opening extending from the thread receiving end of the tube toward the thread discharge end, preferably to the point along the axis corresponding to the surface area where the maximum fixing temperature is reached. In this hollow portion of the tube, the axial opening or bore becomes progressively smaller in a direction proceeding from the thread receiving end to the thread discharge and such that the annular cross-sectional wall thickness of the tube diminishes progressively in the opposite direction. By providing means to heat the tube at its thread discharge end, it will be readily observed that heat will be conducted to the outer thread-contacting surface of the tube and that the temperature of this outer surface will gradually decrease because of heat losses in a direction away from the thread discharge end of the tube, i.e. in a direction opposite to the thread travel.

With reference to the drawing, FIG. 1 illustrates one heating device constructed in accordance with the invention in which the outer or thread-contacting surface of the tube has a substantially cylindrical shape. FIG. 2 illustrates an alternative embodiment with a substantially frusto-conical shape. An especially preferred elongated tube is illustrated in FIG. 3 and is also shown with the remaining essential apparatus in FIG. 4. The preferred tube has a substantially frusto-conical shape defined by its outer surface at the lower or thread discharge end, tapering away therefrom. At its upper or thread receiving end the tube is outwardly flared to give a hyperbolic surface shape. In all of these embodiments, the thread discharge end of the tube is internally heated by an electrical resistance heating element R.

The process of the invention is advantageously carried out in accordance with FIG. 4 wherein the thread T is supplied by the feed rolls 1 and drawn under stretching tension by the draw rolls 2. Heating and stretching of the thread takes place on the surface of the tubular heating device 3 which is mounted in any convenient manner between the feed and draw rolls. It is helpful to provide this heating device with a rotatable elliptical head or rim 4 at the thread receiving end so as to fix the point at which the thread engages or runs on to the tube. The thread then follows a spirally advancing line along the surface of the tube to the thread discharge end, the thread being maintained in continuous and uninterrupted contact with the tube because of the stretching tension imparted by the feed and draw rolls. The length of this contact can of course be varied by the shape of the tube as well as its length and diameter. The number of turns of the thread around the tube can also be varied to provide the desired length of contact. In most cases, one complete turn is satisfactory.

The lower or discharge end of the elongated tube 4 is shown to have an axial recess or insert containing an electrical resistance heating element R which is employed to heat this end of the tube on its surface to that temperature required to fix or stabilize the thread, but not higher than the maximum fixing temperature which is dependent upon the particular synthetic material being processed. The tube is preferably constructed of a heat-conducting metal or two or more different metals, thereby conducting heat to the surface of the tube and toward the thread receiving end of the tube. Because of the gradually diminishing cross-sectional area of the annular walls in the upper or hollow portion of the tube, the surface temperature correspondingly becomes lower through heat conduction and radiation in the direction of the unheated thread receiving end. This temperature drop would occur to some extent even with a constant annular wall thickness, but a continuous diminuation of this thickness is necessary to obtain a sufficient temperature gradient over a relatively short distance.

Any suitable metal can be employed in constructing the tubular heating device such as iron, Bessemer steel, chromium steel, nickel steel and the like. It is especially advantageous for reasons of cost to construct the tube with an inner core of a relatively inexpensive metal such as iron and to use an outer surface layer or mantle of a more expensive but corrosion resistant metal such as chromium steel. Where a very high temperature drop is required over a. relatively short length of the tube, different metals with decreasing coeflicients of heat conductivity can be arranged in longitudinal sections of the tube, e. g. the lower portion being constructed of iron and the upper portion of chromium steel.

The tubular bodies illustrated in FIGS. 1-4 are given merely by way of example of the heating device required by the invention. Minor variations in shape and construction can readily be made without departing from the spirit or scope of the invention. For example, instead of an electrical resistance heating element, the temperature of the tube surface can also be regulated by means of a fluid heat exchange medium, e.g. a gas, vapor, or liquid capable of being maintained at the maximum fixing or stabilizing temperature. In this case the lower or thread discharge end can be provided with a metal block or similar insert containing a continuous fluid passageway for circulation of the heat exchange medium, this passageway being in fluid connection with external inlet and outlet conduits. In eifect, the tubular device of the invention then acts as a means for indirect heat exchange between the heating fluid and the thread which lies in contact with the outer surface of the tube.

While many combinations and variations in the surface temperature of the tubular heating device are possible and are contemplated within the scope of the present invention, it is essential that the thread discharge end of the tube be heated to the required fixing temperature and that the surface temperature then progressively drop to a suitable drawing temperature at the thread receiving end. The apparatus described above provides an especially useful means for accomplishin this result. Thus, one special advantage of the invention is that the thread provides its own uniform and gradual stretching along the surface of the tube in accordance with its degree of plastification or extensibility, the friction of the heated surface and the tension applied by the feed and draw rolls. Optimum results in the textile and physical properties of the thread are thusv obtained, and such results are believed to be caused by the fact that there is no intermittent cooling of the thread between the drawing temperature and the fixing temperature. The apparatus of the invention is especially advantageous in that the tubular heating device can be directly mounted without difficulty on all of the commer cially known stretching or drawing equipment. The very small space requirement of the tubular heating device is an added advantage.

The term thread is employed herein with reference to both monofilaments and bundles of a plurality of filaments in the form of a yarn, tow, cable or the like. The term drawing is employed with the same meaning as the term stretching. Likewise, the terms fixing and stabilizing are both employed to refer to the heat treatment of a thread whereby certain thermal properties or characteristics are rendered more stable. Such thermal properties are often different with different synthetic materials even though the processing steps remain substantially identical. It will further be understood that the present invention is concerned with drawing and fixing threads by the so-called dry heating method as distinguished from wet heating in a liquid bath or the like.

The present invention is further illustrated by the following example in connection with FIG. 4 for the thermal stretching and fixing or stabilizing of polyethylene terephthalate. The invention is not to be limited to this example which is given merely as one preferred embodiment of both the apparatus and process.

EXAMPLE A polyethylene thread of 75 denier (36 individual filaments) obtained in a conventional spinning or extruding process is removed from a storage spool or bobbin (not shown) by the pair of clamping feed rolls 1. The thread then runs on the tubular heating device 3 at a point determined by the elliptical head 4 and is entwined or spirally wound on the surface of the tubular body. The draw rolls 2 are operated at a rate of speed four times faster than the feed rolls 1 so as to draw off the thread under tension with stretching to about four times the original length of the thread.

The tubular body 3 has an interior core composed of iron and a chromium-plated mantle or outer surface to engage the spirally wound thread. The overall length of the tube is 12 cm. with a minimum outer diameter adjacent the thread receiving end of 51 mm. and a maximum outer diameter at the thread discharge end of 55 mm. The tube is provided with a hollow axial bore which is cylindrical in shape and has a diameter of 45 mm. Thus, the maximum wall thickness at the lower or discharge end of the tube is 5 mm., and this thickness decreases progressively to a minimum of about 3 at the upper end. An electrically heated metal block R is inserted into the lower end of the axial bore or opening, and the surface of the tube at this point is heated to 200 C. Because of heat losses, the temperature of the tube surface diminishes upwardly to the thread receiving end, at which point the temperature is 70 C.

In passing or spirally advancing on the tube surface, the thread occupies a linear distance of about 1-4 cm. and its rate of travel, as determined by the draw roll, is about 40 cm./sec.

After completion of the thermal stretching and stabilization on the heated tube, the thread has a strength of 5.5 grams/ denier and an elongation of 16%. The thread is especially distinguished by a low heat shrinkage capacity of only 7.2% as measured in boiling water for one hour.

The same or similar apparatus with only minor modifications can also be used with other synthetic filamentary materials, e.g. polyamides, polyacrylonitrile, polyolefines and the like which are heat-stretchable and which require both drawing and stabilization at elevated temperatures. The only substantial variation in the process is in the particular temperature conditions, i.e. the lower drawing temperature and the higher fixing or stabilizing temperature. The following table gives some representative examples of typical synthetic materials and the temperatures within which each end of the heated tube is preferably maintained. The lowest temperature for drawing in each case represents a minimum temperature condition, and the highest temperature for fixing represents the so-called maximum fixing or stabilizing temperature. In order to avoid damage to the synthetic material, this maximum fixing temperature should not be exceeded. The values given in the table as well as similar temperature conditions for other materials are generally well known in the art or can be readily determined for the purposes of the invention.

Table Drawing temp, C. Fixing temp., 0.

Synthetic Range Preferred Range Preferred (appr0x.) (approx) (1) Polyethylene terephthalate -120 136-190 165 (2) Nylon 90-180 180-215 210 (3) Polycaprolactam 20-110 80 160-210 190 (4) Polyacrylorutrrle 100-140 130-180 (5) Polyethylene 60-115 110 100-115 110 The invention is hereby claimed as follows:

1. An improved apparatus for heating and drawing threads, which comprises: means to supply thread; means for drawing off said thread at a more rapid rate than the rate at which the thread is supplied by said supply means; and a heating device positioned in the path of said thread between said supply means and said drawing off means, said heating device comprising an at least partially hollow, elongated, heat-conducting tube adapted to receive said thread at one end for thread travel in spiral winding contact along the outer surface of said tube and to discharge said thread at the opposite end, the longitudinal axis of said tube coinciding approximately with the linear direction of said thread path and the annular cross-sectional wall thickness of said tube in the hollow portion thereof diminishing progressively from said discharge end to said receiving end, and means to heat said tube at said discharge end for conductance of heat radially to the outer thread-contacting surface of the tube and longitudinally to said receiving end.

2. Improved apparatus as claimed in claim 1 wherein the outer surface of said heat-conducting tube has a substantially cylindrical shape.

3. Improved apparatus as claimed in claim 1 wherein the outer surface of said heat-conducting tube has a substantialy frusto-conical shape.

4. Improved apparatus as claimed in claim 1 wherein the outer surface of said heat-conducting tube has a substantially frusto-conical shape tapering away from the thread discharge end of said tube and a hyperbolic outwardly flaring shape at the thread receiving end of said tube.

5. In a method of heating and drawing threads wherein a thread must first be heated at a lower drawing temperature and subsequently at a higher fixing temperature under stretching tension, the improvement which comprises: running the thread in a linear path onto one end of an elongated body made up of substantially cylindrical crosssections; simultaneously heating and drawing said thread in spiral winding contact along the continuous longitudinal surface of said elongated body to the opposite end thereof where said thread is run off under tension in a linear path; said linear paths of the thread coinciding approximately with the longitudinal axis of said elongated body; heating said elongated body at the thread run-off end thereof to a surface temperature suitable for fixing said thread; and conducting heat through said elongated body toward the thread run-on end thereof such that said longitudinal surface is heated in a continuously decreasing temperature gradient from said run-off end to said run-0n end.

References Cited in the file of this patent UNITED STATES PATENTS 2,874,410 Kinney Feb. 24, 1959 2,988,783 Miller et a1 June 20, 1961 2,993,260 Boerma et al. July 25, 1961 3,001,236 'Maier et a1. Sept, 26, 1961 

1. AN IMPROVED APPARATUS FOR HEATING AND DRAWING THREADS, WHICH COMPRISES: MEANS TO SUPPLY THREAD; MEANS FOR DRAWING OFF SAID THREAD AT A MORE RAPID RATE THAN THE RATE AT WHICH THE THREAD IS SUPPLIED BY SAID SUPPLY MEANS; AND A HEATING DEVICE POSITIONED IN THE PATH OF SAID THREAD BETWEEN SAID SUPPLY MEANS AND SAID DRAWING OFF MEANS, SAID HEATING DEVICE COMPRISING AN AT LEAST PARTIALLY HOLLOW, ELONGATED, HEAT-CONDUCTING TUBE ADAPTED TO RECEIVE SAID THREAD AT ONE END FOR THREAD TRAVEL IN SPIRAL WINDING CONTACT ALONG THE OUTER SURFACE OF SAID TUBE AND TO DISCHARGE SAID THREAD AT THE OPPOSITE END, THE LONGITUDINAL AXIS OF SAID TUBE COINCIDING APPROXIMATELY WITH THE LINEAR DIRECTION OF SAID THREAD PATH AND THE ANNULAR CROSS-SECTIONAL WALL THICKNESS OF SAID TUBE IN THE HOLLOW PORTION THEREOF DIMINISHING PROGRESSIVELY FROM SAID DISCHARGE END TO SAID RECEIVING END, AND MEANS TO HEAT SAID TUBE AT SAID DISCHARGE END FOR CONDUCTANCE OF HEAT RADIALLY TO THE OUTER THREAD-CONTACTING SURFACE OF THE TUBE AND LONGITUDINALLY TO SAID RECEIVING END. 